A range in which a focus lens is to be moved is set; the focus lens is moved within the set range; an in-focus state is determined based on output signals from an image sensing unit which are obtained in association with the movement of the focus lens within the range; and the focus lens is driven so that an object image is brought into focus. When a difference between the positions of the focus lens, at which the plurality of images are brought into focus, is equal to or lower than a preset threshold, the range will be set to be wider than a range in the case where the difference exceeds the threshold.